Controllable pitch propeller



March 14, 1961 w. B. VOISARD CONTROLLABLE PITCH PROPELLER 2 Sheets-Sheet1 Filed July 30, 1958 FIG-1 INVENTOR. WALTER B. VOISARD ATTORNEYS March14, 1961 w. B. VOISARD 2,974,729

CONTROLLABLE PITCH PROPELLER Filed July 30, 1958 2 Sheets-Sheet 2INVENTOR. WALTE R B. VOI SAR D ATTORNEYS 2,974,729 CONTROLLABLE PITCHPROPELLER Walter B. Voisard, Dayton, Ohio, assignor to McCauleyIndustrial Corporation, Dayton, Ohio, a corporation of New York FiledJuly 30, 1958, Ser. No. 751,912

11 Claims. (Cl. 170-,-160.32)

This invention relates to controllable pitch propellers for aircraft. 1The invention has particular relation to a propeller control systemof-the type wherein a hydraulic motor responsive to engine speed isarranged to urge the propeller blades in the direction to reduce theirpitch against the biasing force ofa control spring urging the bladesto-" wards a maximum pitchposition, which may be full feathered positionor whatever other maximum pitch' position is desired.

In a propeller control system of this type, wheneverthe hydraulicpressure fails or is otherwise insufilcient to counterbalance theforceof the control spring, the spring will automatically move the blades totheir maximum pitch position unless some provision is made to thecontrary.- This may be a desirable result for a feathering propeller inthe event of engine failure in flight, since it will automaticallyfeather the propeller upon such failure of the hydraulic controlpressure. It is less desirable, however, if the same action occurs whenthe engine is shut off with the plane on the ground, since this meansthat the next time the engine is subsequently started, it must be doneagainst the load created by having the propeller blades in their maximumpitch position in which they offer maximum resistance to turning overthe engine.

It is a primary object of the present invention to provide a novel,simple and effective stop mechanism for incorporation with a propellercontrol system of the type outlinedabove which isso constructed andarranged that it will oiier no interference to operation of the controlsystem when the plane is in flight, but when the engine is shut ofiwhile the plane is on the ground, it will hold the blade in a desiredlow pitch position facilitating restarting of the engine.

It is particularly an object of the invention to provide a stopmechanism as outlined-above-which is independent of the engine speed butis responsive to acceleration and deceleration of the engineirrespective of the actual engine speed.

A further object of the invention is to provide a stop mechanism asoutlined above wherein a latching member is mounted in the rotary hubstructure and is normally biased to a latching position wherein it willengage a fixed stop to block movement of the piston in the direction toincrease blade pitch beyond an intermediate position corresponding to--a relatively low pitch, and wherein an inertia weight responsive todeceleration of the engine is effective to move this latching member toa release position to provide for feathering of the propeller.

It is also an object of the invention to provide a stop mechanism asoutlined above which is of such structure and operating characteristicsthat all the moving parts thereof may be mounted within the hydraulicmotor component of the propeller control system and will therefore beimmersed in hydraulic fluid during use for maintained lubrication aswell as-protection against corrosion and other damage.

; Additional objects and advantages of the invention will 2,974,729Patented Mar. 14, 196 1 ice be apparent from the following description,the accompanying drawings and the appended claims.

In the drawings- Fig. 1 is a partially diagrammatic view generally inaxial section through an airplane hub structure constructed inaccordance with the invention;

Fig. 2 is an enlarged fragment of Fig. 1 showing parts of the stopmechanism in section and in the relative positions which they occupywhen the propeller is being feathered;

Fig. 3 is an enlarged view taken as indicated by the line 3-3 of Fig. 2;

when the propeller is accelerating or blocked in interforward end of theengine shaft 12. The hub 10 carries piston rod 23 to the interior of thecylinder 20 from the usual pump 40 and reservoir 41 through the line 42vand Fig. 4.is a fragmentary section on the line 4-4 of Fig. 3 on areduced scale; and

Fig. 5 is a fragmentary view similar to Fig. 3 but show ing the parts inthe relative positions which they occupy mediate pitch position.

Referring to the drawings, which-illustrate a preferred' embodiment ofthe invention, Fig. 1 shows at 10 the hub of an airplane propeller whichis secured at 11 to the the mountings 13 for the roots of the propellerblades indicated diagrammatically at 15, and the mountings 13 arerotatable on the hub 10 to change the pitch of the blades.-

Fig. 1 also illustrates diagrammatically at 16 a counterweight such asshould be attached as at 17 to each blade" mounting in such manner as toovercome thecentr'ifugal' twisting movement of the blade.

The system for controlling the pitch of the blades 15. includes ahydraulic motor comprising a cylinder 20; which is mounted on the frontend of the hub 10 as by bolts 21 to form a portion of the rotary hubstructure The complementary piston 22 in cylinder 20 is secured on' theforward end of a hollow piston rod 23, as by bolts 24, J

and the piston 22 includes a tubular sleeve 25 which forms an extensionof the piston rod 23. The piston rod 23 is connected by a link 26 witheach of the blade mountings} 13 in such manner that when the piston 22is at its limitposition of movement outwardly of the cylinder 20, to theposition.

The low pitch stop for the piston 22 limiting its movement outwardly ofthe cylinder 20 is formed by a flange. portion 30 of the hub 10 whichprojects radially inwardly beyond the inner wall of the cylinder. Thepiston 22 is continually biased in the direction to increase the bladejpitch by one or more control springs 33 mounted in thehub structurebetween the piston 22 and the guide flange 35 at the rearward end ofthehub 10 through which the piston rod 23 extends for reciprocation withthe piston.- The force opposing the spring 33 to urge the piston 22 in Pthe direction to decrease pitch is provided by hydraulicfluid suppliedthrough the hollow crank shaft 12 and the transfer bearing 43.

A governor 44 and governor valve 45, which may be of conventionalconstruction, control the pressure supply,

to the cylinder 20 in accordance with engine speed to change the bladepitch as required to maintain the engine speed constant. Thus so long asthe engine speed is below the control speed for which the governor isset, the pressure fluid will be supplied to cylinder 20 to maintain thepiston 22 in the minimum blade'pitch position- When-; ever the enginespeed rises above the control speed, the.

- thecylinder and thus to increase the blade pitch until .the

resulting increased load has slowed down the engine to the control speedrange.

If the engine should fail in flight, or if the hydraulic fluid supplyshould fail for any other reason such as a broken oil line, theresulting rapid loss of pressure in cylinder 20 will allow the spring 33to move the piston 22 all the way to its maximum or feather pitchposition. Similarly feathering can be initiated by the pilot by shiftingthe governor valve 45 through the manual control 46-47 to its featherposition wherein it connects the cylinder 20 directly with the reservoir41 and thus relieves the entire hydraulic force opposing the controlspring 33. However, the same result will occur when the engine is shutoff with the plane on the ground and the hydraulic fluid leaks back tothe reservoir. This would mean that the blades would be in maximum pitchposition when the engine is to be started again, which would offer themaximum resistance to rotation of the engine shaft, and it is thisresult which the present invention prevents by the provisions of a stopmechanism assuring' that the blades remain in a relatively low pitchposition after the engine is shut oflf.

Referring to Figs. 1-2, a stop member in the form of a stud 50 ismounted in the inner or forward end wall of the cylinder 20 as by screws51, and this stud may be tubular as shown for decreased weight. The stud50 is proportioned for telescoping engagement with the hollow piston rod23 when the piston moves inwardly of the cylinder, and an annularshoulder 52 near the base of the stud 50 forms the feather pitch stopfor inward movement of the piston and is in position for directengagement by the forward end of the sleeve portion 25 of the piston.The stud 50 is provided with a through slot 53 which extends throughoutthe major portion of its length beyond the stop 52. The outer orrearward end face 55 of the stud 50 is therefore in two sections, andthese sections form a shoulder which acts as an intermediate pitch stopfor the piston 22 and which is utilized selectively for this purpose asnow described.

An inertia Weight 60 in the nature of a flywheel is rotatably mounted onthe piston sleeve 25 as by a ball bearing 61. This weight 60 includes ahub portion 62 which is directly mounted on the bearing 61 and isconnected by a relatively thin radially extending web portion 63 withthe outer portion 60 in order to provide the major proportion of theweight of this member at the maximum radial distance from the axis ofthe piston sleeve 25 while reducing to a practical minimum the overallweight of this member as a whole. The hub portion 62 of the member 60 isprovided with opposed slots 64 which receive the ends of a radiallyarranged bar 65 as shown in Fig. 4, and the piston sleeve 25 is providedwith opposed slots 66 which receive this bar 65 therethrough. A snapring 67 holds the bar 65 in place in the slots 64.

As illustrated in Figs. 3 and 5, the slots 66 cooperate with the bar 65to limit the rotational movement of the weight 60 on the sleeve 25 to asmall angular range shown as about 45. This movement, however, issufiicient to move the bar 65 into and out of alignment with the slot 53in the stud 50. Thus in assembling the cylinder and piston, the partsare so aligned that when the weight 60 is at its limit ofcounterclockwise rotation as viewed in Fig. 3, the bar 65 will bealigned with the slot 53 for free entry therein upon movement of thepiston to the left in Fig. 2, and this is the release position of theweight 60 and bar 65. When the weight 60 is rotated in clockwisedirection on the sleeve 25 to its other limit position established bythe bar 65 and slots 66, the bar 65 will be aligned with the end face 55of the stud 50 for engagement thereon to block further movement of thepiston to the left in Fig. 2, and this is the latching position of theweight 60 and bar 65 as shown in Fig. 5.

In the arrangement of the parts as viewed in Fig. 3, the direction ofrotation of the hub structure is counterclockwise. It willtherefore beseen that the inertia forces effective on the weight 60 will urge it inclockwise direction to a retarded position establishing the latchingposition of the bar when the propeller is accelerating, but will urgethe weight 60 in counterclockwise direction to an advanced positionlocating the bar 65 in its release position when the propeller isdecelerating. In addition, a torsion spring 70 is mounted beneath thesleeve 25 and the weight 60 for urging the weight 60 in clockwisedirection towards its latching position.

The inner end 71 of the spring 70 is received in one of the slots 66 andheld in place axially by a snap ring 72, and the outer end 73 of thespring 70 is received in one of a plurality of bores 74 in the hub 62.The spring 70 should be of such force that it will hold the weight 60 inthe latching position of the bar 65 when the hub is stationary orrotating at a constant positive speed but should be insufiicient toprevent movement of the weight 60 to, the release position of bar 65whenever the hub is decelerating. These conditions are readily achievedby winding the spring 70 to the desired tension while assembling theparts and then inserting the end 73 thereof in the proper selected bore74.

The stop mechanism of the invention will have no effect on the normaloperation of the airplane in flight. More specifically, the propellerwill increase or decrease pitch as required by the governor, but thisvariation will ordinarily be within a relatively low angular range, forexample from 9'to 26. The stud 50 will be proportioned in accordancewith this normal range so that its end face 55 would be engaged by thebar 65 at a slightly greater pitch, for example 30. Therefore, while theweight 60 will during normal operation move the bar 65 back and forthbetween its latching and release positions, the blade pitch will notincrease sufiiciently to permit the bar 65 to reach the stud face 55.

If on the other handa condition should develop during flight whichrequires feathering of Y the propeller, the feathering operation isinitiated by moving the control 47 to its feathering position in whichit shifts the valve 45 to the position connecting the interior of thecylinder 20 directly with the reservoir 41 in order to effectcompletereliefof the pressure supply in the cylinder. The spring 33 willtherefore be free to move the piston inwardly of the cylinder, and thepropeller will immediately begin to decelerate, due both to the increasein pitch as well as to the fact that the motor will normally be cut offin conjunction with feathering. Deceleration of the hub will produce aninertia force effective on the weight 60 in the direction to move thebar 65 to its release position in alignment with the slot 53, andtherefore the piston will be free to move to its full feathered positionestablished by the stop shoulder 52.

Unfeathering of the propeller in flight may be accomplished by movingthe control handle 47 out of its feathering position and then turningthe engine over with the usual starter. As soon as sufficient pressureis built up in this way to move the piston away from stop 52, thepropeller will begin to windmill, and the resulting rapid pressurebuild-up will move the piston back to low pitch position. The bar 65will have no effect on this operation, since it will simply slidethrough the slot 53 until it is clear of the stud 50.

As noted, while it is desired in accordance with the invention that thepropeller be free to feather when the engine is shut off and thehydraulic pressure is relieved in flight, it is also desired thatfeathering be prevented when the engine is shut off while the airplaneis on the ground. Under these conditions, the control handle 47 isretained in the position causing the hydraulic fluid to be continuouslysupplied to the cylinder 20, and the control system will thereforeretain the propeller at minimum pitch, with the piston 22 in contactwith the stop 30, until the engine is completely dead. Furthermore, thispressure will remain effective for an appreciable intervahnamelya minuteor more, until it is finally lost as 5 a result of gradual leakageofthehoil back to the reservoir.41.'

During the above operation while the engine is decelerating, the inertiaforce on the weight 60 will retain the bar 65 in its release position,but thisis not significant because the piston is held on its low pitchstop as just described. However, when the engine is completely dead,there will be no more inertia force on the weight 60, and the spring 70will therefore be able to return it to the latching position of the bar65. This return movement will take place before the pressure supply inthe cylinder has leaked away, and therefore when the spring 33 isfinally able to move the piston inwardly of the cylinder, the bar 65will be in latching position to engage on the stud face 55 and therebyto block further movement of the piston beyond the intermediate pitchposition thus established.

The invention accordingly providesa stop mechanism ofiering a variety ofimportant practical advantages. It is simple to construct and install,it requires a minimum of maintenance, and it is independent of enginespeed and: responsive only to acceleration and deceleration of theengine. It is also simple to proportion the working parts, andparticularly the stud 50, to establish whatever intermediate pitchposition is desired for a particular operating range for the propeller,and it is not a serious disadvantage if such position be within theoperating range. it should also be noted that the operating parts arenot limited to installation within the cylinder 20 so long as theoperating principles of the invention are maintained, but theillustrated arrangement does offer the special advantage that all themoving parts are located within the hydraulic pitch control motor wherethey are constantly immersed in oil and thus kept thoroughly lubricatedas well as protected against corrosion and possible interference byweather conditions such as icing which could affect them if they were inan exposed location. All these advantages are provided in the inventionwithout aiiecting the normal operation of the control system with whichit is used.

Cross reference is made to my copending application Serial No. 827,963,filed July 17, 1959, and assigned to the same assignee as thisapplication.-

While the form of apparatus herein described constitutes a preferredembodiment of the invention, it is to be understood that the inventionis not limited to this precise form of apparatus, and that changes maybe made therein without departing from the scope of the invention whichis defined in the appended claims.

What is claimed is:

1. In a control system for the blades of an adjustable pitch propellerhaving a drive engine, the combination of a rotary hub structureincluding adjustable supporting means for said blades, a hydraulic motorwithin said hub structure including a stationary cylinder and a movablepiston, means connecting said piston with said supporting means todecrease the pitch of said blades in response to movement of said pistonoutwardly of said cylinder and to increase said blade pitch to featheredposition in response to movement of said piston inwardly of saidcylinder, a control spring arranged to bias said piston inwardly of saidcylinder, means including a line connected with said cylinder forsupplying hydraulic pressure fluid to member supported on said hubstructure for movement relative thereto betweena release positionoifering no resistance to the movement of said piston and a latchingposition blocking said piston from movement inwardly 5 structure forbiasing said latching member to said latch ing position to block inwardmovement of said piston beyond said intermediate position when saiddrive engine is shut ofi while said pressure fluid is being supplied tosaid cylinder, inertia means mounted on said hub structure for movementrelative thereto in response to deceleration of said hub structure, andmeans connecting said latching member with said inertia means forcausing said latching member to move against said biasing means to saidrelease position in response to said movement of said inertia means toprovide for feathering of said propeller when said pressure fluid supplyis relieved by operation of said valve means.

2. In a control system for the blades of an adjustable pitch propellerhaving a drive engine, the combination of a rotary hub structureincluding adjustable supporting means for said blades, a hydraulic motorwithin said hub structure including a' stationary cylinder and a movablepiston, means connecting said piston with saidsupporting means todecrease the pitch of said blades in response to movement of said pistonoutwardly of said cylinder and to increase said blade pitch to featheredposition in response to movement of said piston inwardly of saidcylinder, a control spring arranged to bias said piston inwardly of saidcylinder, means including a line connected with said cylinder forsupplying hydraulic pressure fluid to said cylinder to move said pistonagainst said control spring, selectively operable valve means in saidline for relieving said pressure fluid supply, a stop mechanism forselectively blocking increase in the pitch of said blades beyond apredetermined low pitch including a latching member supported on saidpiston for movement relativethereto between a release position ofien'ngno resistance to the movement of said piston and a latching positionblocking said piston from movement inwardly of said cylinder beyond aposition corresponding to said predetermined low blade pitch, meansconnected between said latching member and said hub structure forbiasing said latchingmember to said latching position to block inwardmovement of said piston beyond said intermediate position when saiddrive engine is shut ofl? while said pressure fluid is being supplied tosaid cylinders, inertia means mounted on said hub structure for movementrelative thereto in response to deceleration of said hub structure, andmeans connecting said latching member'with said inertia means forcausing said latching member to move against said biasing means to saidrelease position in response to said movement of said inertia means toprovide for feathering of said propeller when said pressure fluid supplyis relieved by operation of said valve means;

3, In a control system for the blades of an adjustable pitch propellerhaving a drive engine, the combination of a rotary hub structureincluding adjustable supporting means for said blades, a hydraulic motorwithin said hub structure including a stationary cylinder and a movablepiston, means connecting said piston with said supporting means todecrease the pitch of said blades in response to movement of said pistonoutwardly of said cylinder and to increase said blade pitch to featheredposition in response to movement of said piston inwardly of saidcylinder, a control spring arranged to bias said piston inwardly of saidcylinder, means including a line connected with said cylinder forsupplying hydraulic pressure fluid to said cylinder-to move said pistonagainst said control spring, selectively operable valve means in saidline for relieving said pressure fluid supply, a stop mechanism forselectively blocking increase in the pitch of said blades beyond apredetermined low pitch including a latching member supported on saidhub structure for rotational movement relative thereto between a releaseposition oifering no resistance to the movement of said piston and alatching position blocking said piston from movement inwardly of saidcylinder beyond a position corresponding to said predetermined low bladepitch, means .con-

nected between said latching member and said hub structure for biasingsaid latching member to said latching position to block inward movementof said piston beyond said intermediate position when said drive engineis shut off while said pressure fluid is being supplied to saidcylinder, inertia means mounted on said hub structure for movementrelative thereto in response to deceleration of said hub structure, andmeans connecting said latching member with said inertia means forcausing said latching member to move against said biasing means to saidrelease position in response to said movement of said inertia means toprovide for feathering of said propeller when said pressure fluid supplyis relieved by operation of said valve means.

4. In a control system for the blades of an adjustable pitch propellerhaving a drive engine, the combination of a rotary hub structureincluding adjustable supporting means for said blades, a hydraulic motorwithin said hub structure including a stationary cylinder and a movablepiston, means connecting said piston with said supporting means todecrease the pitch of said blades in response to movement of said pistonoutwardly of said cylinder and to increase said blade pitch to featheredposition in response to movement of said piston inwardly of saidcylinder, a control spring arranged to bias said piston inwardly of saidcylinder, means including a line connected with said cylinder forsupplying hydraulic pressure fluid to said cylinder to move said pistonagainst said control spring, selectively operable valve means in saidline for relieving said pressure fluid supply, a stop member in saidcylinder for limiting movement of said piston in the direction ofincrease the pitch of said blades beyond an intermediate positioncorresponding to a predetermined low pitch, a latching member supportedon said piston for movement relative thereto between a release positionwith respect to said stop member offering no resistance to the movementof said piston and a latching position for engagement with said stopmember locking said piston from movement inwardly of said cylinderbeyond said intermediate position, means connected between said latchingmember and said hub structure for biasing said latching member to saidlatching position to block inward movement of said piston beyond saidintermediate position when said drive engine is shut off while saidpressure fluid is being supplied to said cylinder, inertia means mountedon said hub structure for movement relative thereto in response todeceleration of said hub structure, and means connecting said latchingmember with said inertia means for causing said latching member to moveagainst said biasing means to said release position in response to saidmovement of said inertia means to provide for feathering of saidpropeller when said pressure fluid supply is relieved by operation ofsaid valve means.

5. In a control system for the blades of an adjustable pitch propellerhaving a drive engine, the combination of a rotary hub structureincluding adjustable supporting means for said blades, a hydraulic motorwithin said hub structure including a stationary cylinder and a movablepiston, means connecting said piston with said supporting means todecrease the pitch of said blades in response to movement of said pistonoutwardly of said cylinder and to increase said blade pitch to featheredposition in response to movement of said piston inwardly of saidcylinder, a control spring arranged to bias said piston in- Wardly ofsaid cylinder, means including a line connected with said cylinder forsupplying hydraulic pressure fluid to said cylinder to move said pistonagainst said control spring, selectively operable valve means in saidline for relieving said pressure fluid supply, a stop member in saidcylinder for limiting movement of said piston in the direction toincrease the pitch of said blades beyond an intermediate positioncorresponding to apredetermined low, pitch, an inertia .weight: mountedon-said 'pistonfor oscillating movement between advanced and retardedpositions in response to deceleration and acceleration respectively ofsaid hub structure, a latching member supported on said inertia weightfor movement therewith between a release position corresponding to saidadvanced position of said weight and out of line with said stop memberand a latching position corresponding to said retarded position of saidweight and in line with said stop member for engagement therewith, andmeans connected between said piston and said weight biasing said weightto said retarded position to eifect blocking of inward movement of saidpiston beyond said intermediate position by said latching and stopmembers when said drive engine is shut off while said pressure fluid isbeing supplied to said cylinder.

6. In a control system for the blades of an adjustable pitch propellerhaving a drive engine, the combination of a rotary hub structureincluding adjustable supporting means for said blades, a hydraulic motorwithin said hub structure including a stationary cylinder and a movablepiston having a hollow piston rod, means connecting said piston withsaid supporting means to decrease the pitch of said blades in responseto movement of said piston outwardly of said cylinder and to increasesaid blade pitch to feathered position in response to movement of saidpiston inwardly of said cylinder, a control spring arranged to bias saidpiston inwardly of said cylinder, means including a line connected withsaid cylinder and means responsive to the operation of said drive enginefor supplying hydraulic pressure fluid to said cylinder to move saidpiston against said control spring, a stud mounted on the inner end wallof said cylinder in position for telescoping engagement with said pistonrod upon movement of said piston inwardly of said cylinder and includinga shoulder adapted to form a stop for said piston, a latching member forsaid piston, means mounting said latching member on the inner face ofsaid piston for movement relative thereto between a release position outof line with said shoulder of said stud and a latching positionoverlying said shoulder for engagement therewith, said stud beingproportioned for engagement by said latching member with said shoulderupon movement of said piston to an intermediate low blade pitch positionadjacent said limit position, means connected between said latchingmember and said piston for biasing said latching member to said latchingposition to block inward movement of said piston beyond saidintermediate position when said drive engine is shut 011? while saidpressure fluid is being supplied to said cylinder, inertia means mountedon said piston for movement relative thereto in response to decelerationof said hub structure, and means connecting said latching member withsaid inertia means for causing said latching member to move against saidbiasing means to said release position in response to said movement ofsaid inertia means to provide for feathering of said propeller when saidpressure fluid supply is relieved.

7. In a control system for the blades of an adjustable pitch propellerhaving a drive engine, the combination of a rotary hub structureincluding adjustable supporting means for said blades, a hydraulic motorwithin said hub structure including a stationary cylinder and a movablepiston having a hollow piston rod, means connecting said piston withsaid supporting means to decrease the pitch of said blades in responseto movement of said piston outwardly of said cylinder and to increasesaid blade pitch to feathered position in response to movement of saidpiston inwardly of said cylinder, a control spring arranged to bias saidpiston inwardly of said cylinder, means including a line connected withsaid cylinder and means responsive to the operation of said drive enginefor supplying hydraulic pressure fiuid to said cylinder to move saidpiston againstsaid control spring, a stud mounted on-the inner end W811of said cylinder in position for telescoping engagement with said pistonrod upon movement of said piston inwardly ofsaid cylinder, said studhaving a transverse slot therethrough extending substantially the fulllength thereof, a latchingmember for said piston, means mounting saidlatching member on the inner face of said piston for movement relativethereto between a release position in line with said slot and a latchingposition overlying the end face of said stud for engagement therewith,said stud being proportioned for said engagement by said latching memberupon movement of said piston to an intermediate low blade pitch positionadjacent said limit position, means connected between said latchingmember and said piston for biasing said latching member to said latchingposition to block inward movement of said piston beyond saidintermediate position when said drive engine is shut ofl whilesaidpressure fluid isbeing supplied to said cylinder, inertia means mountedon said piston for movement relative thereto in response to decelerationof said hub structure, and means connecting said latching member withsaid inertia means for causing said latching member to move against saidbiasing means to said release position in response to said movement ofsaid inertia means to provide for feathering of said propeller when saidpressure fluid supply is relieved.

8. In a control system for the blades of an adjustable pitch propellerhaving a drive engine, the combination of a rotary hub structureincluding adjustable supporting means for said blades, a hydraulic motorwithin said hub structure including a stationary cylinder and a movablepiston having a hollow piston rod, means connecting said piston withsaid supporting means to decrease the pitch of said blades in responseto movement of said piston outwardly of said cylinder and to increasesaid blade pitch to feathered position in response to movement of saidpiston inwardly of said cylinder, a control spring arranged to bias saidpiston inwardly of said cylinder, means including a line connected withsaid cylinder and means responsive to the operation of said drive enginefor supplying hydraulic pressure fluid to said cylinder to move saidpiston against said control spring, a stud mounted on the inner end wallof said cylinder in position for telescoping engagement with said pistonrod upon movement of said piston inwardly of said cylinder and includinga shoulder adapted to form a stop for said piston, a flywheel mounted onthe face of said piston for relative advanced and retarded rotationalmovement coaxial therewith in response to the inertia resulting fromdeceleration and acceleration respectively of said hub structure, alatching member mounted on said flywheel, means limiting said movementof said flywheel between an advanced release position wherein saidlatching member is out of line with said shoulder and a retardedlatching position I wherein said latching member overlies said shoulderfor engagement therewith, said stud being proportioned for saidengagement by said latching member with said shoulder upon movement ofsaid piston to an intermediate low blade pitch position adjacent saidlimit position, and means connected between said flywheel and saidpiston for biasing said flywheel to said advanced position to blockinward movement of said piston beyond said intermediate position whensaid drive engine is shut ofi while said pressure fluid is beingsupplied to said cylinder.

9. In a control system for the blades of an adjustable pitch propellerhaving a drive engine, the combination of a rotary hub structureincluding adjustable supporting means for said blades, a hydraulicmotor-within said hub structure comprising a cylinder and a relativelymovable piston assembly including a hollow piston rod, means connectingsaid motor with said supporting means to decrease the pitch of saidblade in response to relative outward movement of said piston assemblyand said cylinder and to increase said blade pitch to feathered positionin response to relative inward movement of said piston assembly and saidcylinder, a control spring urging structure, a latching member carriedby said flywheel,

a stop mounted on said hub structure for limiting relative inwardmovement of said cylinder and said piston assembly by engaging saidlatching member, means limiting said movement of said flywheel betweenan advanced release position wherein said latching member is out of linewith said stop and a retarded latching position wherein said latchingmember overlies said stop for engagement therewith, said stop beinglocated for said engagement by said latching member upon relativemovement of said piston assembly and said cylinder to an intermediatelow blade pitch position, and means biasing said flywheel to saidadvanced position to block relative inward movement of said pistonassembly and said cylinder beyond said intermediate position when saiddrive engine is shut off while said pressure fluid is being supplied tosaid cylinder.

10. In a control system for the blades of an adjustable pitch propellerhaving a drive engine, the combination of a rotary hub structureincluding adjustable supporting means for said blades, a relativelymovable cylinder and piston forming a hydraulic motor within said hubstructure, means connecting said motor with said supporting means todecrease the pitch of said blades in response to relative movement ofsaid piston outwardly of said cylinder and to increase said blade pitchto feathered position in response to relative movement of said pistoninwardly of said cylinder, acontrol spring urging relatively inwardmovement of said piston and said cylinder, means including a lineconnected with said cylinder for supplying hydraulic pressure fluid tosaid motor to cause relative movement of said piston and said cylinderagainst said control spring, selectively operable valve means in saidline for relieving said pressure fluid supply, a flywheel mounted insaid hub structure for rotational movement about the axis of said hubstructure, cooperating means carried by said flywheel and said hubstructure establishing a limit position for said rotational movement ofsaid flywheel in the direction opposed to the direction of rotation ofsaid hub structure, means connected between said flywheel and said hubstructure for biasing said flywheel to said limit position,complementary latch means on said hub structure and said flywheelarranged for latching engagement in said limit position of said flywheelblocking said piston and cylinder from relative inward movement beyondan intermediate position corresponding to a predetermined intermediateblade pitch position, and said flywheel and said biasing means beingproportioned to provide for rotational movement of said flywheel againstsaid biasing means away from said limit position in response todeceleration of said hub structure to prevent engagement of said latchmeans and thereby to provide for feathering of said propeller when saidpressure fluid supply is relieved by operation of said valve means.

11. In a control system for the blades or" an adjustable pitch propellerhaving a drive engine, the combination of a rotary hub structureincluding adjustable supporting means for said blades, a relativelymovable cylinder and piston forming a hydraulic motor within said hubstructure, means connecting said motor with said supporting means todecrease the pitch of said blades in response to relative movement ofsaid piston outwardly of said cylinder and to increase said blade pitchto feathered position in response to relative movement of said pistoninwardly of said cylinder, a control spring urging relatively inwardmovement of said piston and said cylinder, means including a lineconnected with said cylinder for supplying hydraulic pressure fluid tosaid motor to cause relative movement of said piston and said cylinderagainst said control spring, selectively operable valve means in saidline for relieving said pressure fluid supply, a flywheel mounted insaid hub structure for rotational movement about the axis of said hubstructure, cooperating means carried by said flywheel and said hubstructure for establishing first and second limit positions for saidrotational movement of said flywheel, means connected between saidflywheel and said hub structure for biasing said flywheel oppositely tothe direction of rotation of said hub structure to said first limitposition, complementary latch means on said hub structure and saidflywheel arranged for relative release in said second position of saidflywheel and for latching engagement in said first limit position ofsaid flywheel blocking said piston and cylinder from relative inwardmovement beyond an intermediate position corresponding to apredetermined intermediate blade pitch position, and said flywheel andsaid biasing means being proportioned to provide for rotational movementof said flywheel against said biasing means to said second limitposition in response to deceleration of said hub structure to providefor feathering of said propeller when said pressure fluid supply isrelieved by operation of said valve means.

References Cited in the file of this patent UNITED STATES PATENTS UNITEDSTATESPATENT OFFICE CERTIFICATION er CORRECTION Patent No, 2 9741 729March 14L 1961 Walter B. Voisard I It is hereby certified that errorappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as corrected below.

Column 7, line 38 for locking read blocking line 66 for "connected readconnecting Signed and sealed this 15th day of August 19610 (SEAL)Attest: ERNEST W, SWIDER DAVID L LADD Attesting Officer Commissioner ofPatents

